1. Field of the Invention
The present invention relates to thermoplastic bag constructions which are characterized by having a modified bottom gusset edge utilizing a plurality of spaced apart heat seals whereby when the bag is open the bag is self-supporting as a result of the stiffening effect of the vertical heat seals.
2. Description of the Prior Art
In the past, free-standing bag constructions have been characterized by having a rectangular base configuration such as the familiar kraft paper bag which, when opened, has a base which is formed from multiple overlapping layers of the bag which are usually adhesively secured together. Attempts have been made to structure thermoplastic film bags in a manner such that they too would be able to stand open and erect on a support surface. Such attempts have been generally unsatisfactory since the thin plastic material, being relatively limp, tends to crease and fold or fall over. Attempts to remedy this have included increasing the thickness of the material from which the bag is formed to thereby stiffen the bag wall. However, the attendant increase of resin material which thickening entails has made such bags uneconomical. U.S. Pat. No. 3,380,646 is illustrative of attempts made in the past to structure thermoplastic bags in order that they would be free-standing. Such prior art bags, however, have been unsatisfactory as a result of disadvantages which are inherent in their material of construction, namely, the resistance of thermoplastic film to permanent creasing and the lack of modulus or stiffness in comparison to paper or other typical bag materials, including aluminum foil and the like.